1. Field of the Invention
The present invention relates to a method for the cementing of well bores and, more particularly, obtaining improved handling with respect to water and/or gas shut-off of cemented well bores.
2. Description of the Prior Art
In the drilling and completion of an oil well, subterranean zones penetrated by well bores are commonly sealed by hydraulic cement compositions. For example, hydraulic cement compositions, which are also known as Portland cement compositions, and which are not soluble in acid, are used in primary cementing operations whereby strings of pipe, such as casings and linings, are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened, substantially impermeable cement therein, which supports and positions the pipe string in the well bore, and seals the exterior surfaces of the pipe string to the walls of the well bore. Hydraulic cement compositions are also utilized in a variety of cementing operations, such as sealing highly permeable zones or fractures in subterranean zones, plugging cracks or holes in pipe strings and the like.
Notwithstanding the petroleum industry's use of acid-insoluble cement in their primary cementing operations, there are instances, such as in subterranean fracturing operations used to repressurize a formation, or in the drilling of well bores in the presence of excessive water and/or gas production, where the use of an acid insoluble cement in the well bore results in major economic, operational, and environmental problems. Well-bores cemented with hydraulic cements which are acid-insoluble cannot be opened by an acidic wash. Other problems which affect production operations are oil reduction, low-flowing well head pressure, and the necessity to expand the capacity of the water separation and water handling facilities to dispose of large volumes of waste water. Unwanted water production from oil wells can also cause secondary problems, such as sand production, corrosion, emulsion formation and scale formation.